1. Field of the Invention
The present invention relates to a method of providing water for use on-board an automobile. More particularly, the present invention relates to operating an electrolyzer on-board an automobile.
2. Background of the Related Art
Catalytic converters are commonly used to reduce unwanted emissions through catalytic combination of the emissions with oxygen from the air. Catalytic combination, often referred to as catalytic combustion, is a flameless process in which mixtures of emissions (or fuel) and air (or oxygen) are passed over a catalyst at a temperature high enough to favor total oxidation of the emissions (or of the fuel). The reaction occurs at the catalyst surface resulting in liberation of energy and production of reaction products. For organic fuels, the reaction products are primarily carbon dioxide and water.
The control and suppression of unwanted emissions created by the operation of an internal combustion engine is a primary consideration for engine designers and vehicle manufacturers because of nearly world-wide governmental requirements regarding acceptable emission levels. Over eighty percent (80%) of the unacceptable emissions or pollutants created by internal combustion engines equipped with catalytic converters occur during cold start operations. These pollutants are emitted for a period of one to three minutes after cold engine starting, in large part because that is the time period required for the catalyst to reach an efficient operating temperature. Therefore, even though the engine exhaust is flowing through the catalytic converter, until the exhaust heats the catalytic converter to its operating range from engine start up, the engine emissions are only slightly catalytically decomposed during that time period.
In order to meet governmental emission standards for internal combustion engine exhaust, a catalytic converter is located in the exhaust stream of the engine. The converter typically includes a canister holding a suitable catalyst, such as a three-way catalytic converter (TWC) catalyst monolith, that will oxygenate unburned, unacceptable components in the exhaust stream including hydrocarbons (HC), their partially oxidized derivatives such as aldehydes and carbon monoxide (CO), and at the same time reduce nitrogen oxides (NOx), after almost stoichiometric fuel bum with oxygen in the cylinders of the engine. The exhaust gas is passed through the catalyst monolith, thereby completing the oxygenation of unburned HC and CO, and the reduction of NOx in the exhaust to convert these unacceptable emissions into acceptable emissions. Certain unacceptable emissions in the exhaust stream, including unburned hydrocarbons and carbon monoxide, require an oxidation reaction to destroy them so that they end up as the corresponding oxides, e.g., water and carbon dioxide. On the other hand, NOx requires a reduction reaction to develop N2 and O2. In fact, the O2 product of this reduction contributes to the oxidation of the HC and CO in the exhaust.
Catalytic converters are typically manufactured by coating a substrate, such as a metal or ceramic material, with a high surface area material, typically a metal oxide media. The catalytic material, such as a noble metal, is then deposited on the high surface area material. In the formation of such a catalytic converter, a sintered, dense and hardened ceramic substrate for example, which can be in the shape of a honeycomb, wagon-wheel, spiral or other molded or shaped objects, or simply be in the form of pellets, is coated with a slurry of the high surface area material, after which the catalyst is applied to the slurry-coated substrate, typically by application of a solution of a salt of that metal.
More particularly, the underlying ceramic substrate can be cordierite, mullite, alumina, lithium aluminosilicates, titania, zircon, feldspar, quartz, fused silica, clays, kaolin clay, aluminum titanate solid solutions, silicates, zirconia, spinels, glasses, glass ceramics, aluminates, and mixture thereof The constituent ceramic materials are generally admixed with binders or shaping agents, processed, molded where applicable, and sintered. Coating of the substrate with the high surface area media can be effected either by immersion or dipping, followed by heat-treating the coated substrate at a temperature between 500xc2x0 C. and 600xc2x0 C. Procedures for depositing a high surface area xe2x80x9cwash-coatxe2x80x9d on the previously sintered ceramic substrate are disclosed, for example, in U.S. Pat. No. 3,824,196. Following application of the slurry of high surface area material, the catalyst is applied in the manner stated above. Alternatively, a single xe2x80x9cwash-coatxe2x80x9d mixture of the high surface area media and the catalytic material can be applied together.
TWC catalysts are currently formulated and designed to be effective over a specific operating range of both lean and rich fuel/air conditions and a specific operating temperature range. These particular catalyst compositions enable optimization of the conversion of HC, CO, and NOx. This purification of the exhaust stream by the catalytic converter is dependent on the temperature of the exhaust gas and the catalytic converter works optimally at an elevated temperature, generally at or above about 300xc2x0 C. xe2x80x9cLight-off temperaturexe2x80x9d is generally defined as the temperature at which fifty percent (50%) of the emissions from the engine are being converted as they pass through the catalyst. The time period between xe2x80x9ccold startxe2x80x9d and reaching the light off temperature is generally referred to as the xe2x80x9clight-off time.xe2x80x9d
The conventional method of heating the catalytic converter is to heat the catalyst by contact with high temperature exhaust gases from the engine. This heating, in conjunction with the exothermic nature of the oxidation reaction occurring at the catalyst, will bring the catalyst to light-off temperature. However, until the light-off temperature is reached, the exhaust gas passes through the catalyst relatively unchanged. In addition, the composition of the engine exhaust changes as the engine heats from the cold start temperature, and the catalyst monolith is typically designed to work best with the composition of the exhaust stream produced at the normal elevated engine operating temperature.
There have been several attempts to shorten or avoid the light-off time of the catalytic converter. Current techniques employ one of the following methods: electrical heating of the exhaust gases and/or of the catalytic converter itself; thermal insulation of the exhaust line and/or the catalytic converter; multi-chambered configurations of the catalytic converter; placing the catalytic converter adjacent to the engine for heating; combustion of fuels upstream of the catalytic converter; and catalytic combination of fuels and oxygen at the catalyst surface. All of these methods have drawbacks and limitations.
Placing the catalytic converter almost immediately adjacent to the engine is not desirable because of the tendency to overheat the catalyst with resulting accelerated degradation of the catalyst. Thermal insulation is also not a desirable option because of the same problems, especially during operation at maximum operating temperature ranges.
Electrical heating of catalytic converters (xe2x80x9cEHCxe2x80x9d) has been a popular proposed method of attempting to preheat the catalyst monoliths. Limitations on the equipment and process, however, affect the utility of this method. The primary limitation on electrical preheating is the electrical energy required by the heater. The typical car battery is not a practical power source to supply the electrical power because the electrical load on the vehicle battery during the period required may exceed the rated battery output. In any event, the load placed on a typical 12 volt vehicle battery will shorten the lifetime of the battery. Also, there is a measurable delay between the time the operator of the vehicle places the ignition switch in the xe2x80x9conxe2x80x9d position and the time the heater brings the catalyst to light-off temperature.
Typically, in the interval between start up and light-off, the exhaust stream is oxygen deficient. Because the catalyst requires oxygen to complete the catalytic reaction, supplemental air must be blown over the catalyst. Even when using a secondary air flow to overcome oxygen deficiency, the secondary air flow must be closely controlled to avoid an excess of oxygen, in which case the catalytic converter is less effective in reducing NOx. However, it should be noted that NOx contributes a very small portion of unacceptable emissions when an engine is cold; most of the cold start emissions that must be dealt with comprise HC, CO and the like.
An alternative to battery powered electrical heating has been to decrease the strain on the power supply by supplying the power directly from an alternator rather than directly from the vehicle battery. An alternator powered, electrically heated catalyst (xe2x80x9cAPEHCxe2x80x9d) still requires a 5 to 10% increase in battery capacity to cope with the EHC start-up scenario. Even with the APEHC system, there is still a concern with respect to battery capacity because electrical heating is needed for an extended period of time, i.e., more than 25-30 seconds. In addition, the maximum alternator power output required in the APEHC system requires a complicated switching mechanism and an altered alternator speed between 2,000 and 4,500 rpm during the heating up time period, and the alternator must be oversized.
The multi-chamber configurations of catalytic converters generally conform to one or two theories. In one multi-chamber configuration, a small portion of catalyst known as a xe2x80x9cstarter catalystxe2x80x9d is positioned upstream from the primary catalyst. This xe2x80x9cstarter catalystxe2x80x9d is generally closer to the exhaust manifold. This location, in conjunction with a smaller thermal mass associated with its smaller size and materials of construction, causes the catalyst to heat much more quickly than the primary catalyst. This configuration, however, is generally unacceptable because the starter catalyst in the exhaust stream creates a higher back pressure which reduces the overall engine efficiency and robs the engine of power output.
Another method of providing multiple chambers in the exhaust flow includes a first catalyst having low temperature characteristics used only during cold start conditions, and, after the catalyst temperature rises to a certain elevated level, the exhaust gas flow is switched to pass through the conventional catalytic converter configuration. A variation of this approach is to run all cold start emissions through a separate absorber (such as a zeolite or a molecular sieve-type substance) where unacceptable emissions are captured and later released back into the exhaust stream. This method, however, is impractical because of the complicated switching mechanism used to divert flow to the absorber, the size and space requirements of the absorber, and the impracticality of releasing the unacceptable emissions from the absorber back into the exhaust stream.
An additional method for reducing cold start emissions runs the engine excessively rich in the cold start condition and ignite the resulting super-rich mixture to directly heat the catalyst. This approach has proved wholly unreliable and has other serious drawbacks, including reduced engine and catalyst life.
Catalytic combination of a fuel with oxygen at the surface of the catalyst generates heat that can rapidly bring the catalytic converter to light off temperature. For example, the introduction of hydrogen to a TWC catalyst can heat portions of the catalyst to 300xc2x0 C. or greater within a period of several seconds. However, the significant amount of hydrogen necessary to cause this rapid, high temperature heating makes it impractical to store enough hydrogen for any large number of heating cycles. Consequently, it is a practical result that hydrogen must be generated onboard the vehicle.
Hydrogen generation using a proton exchange membrane electrolyzer is described by Appleby in U.S. patent application Ser. No. 08/320,171. Appleby teaches the use of an electrolyzer to convert water to hydrogen gas at the cathode. The hydrogen may then be collected and/or dried for use upon demand. However, the continued operation of the electrolyzer is dependent upon the availability of water to the electrolyzer. While the electrolyzer may be provided with a refillable water reservoir located under the hood, this setup leaves the emissions control system reliant upon the user to actually maintain the water level.
Benz et al. (U.S. Pat. No. 5,658,449) teaches a method and a device for nitrogen oxide reduction in a vehicle""s exhaust gas by its reduction with hydrogen gas on a catalyst mounted in the exhaust system. Benz et al. proposes two methods of generating the required amount of hydrogen, via electrolysis of water aboard the vehicle, or via chemical production of hydrogen from a fuel, e.g., methanol, gasoline, or diesel fuel, via the well-known steam reforming reaction. Benz et al. also teaches that, in association with the former approach, the water required by an electrolyzer may be recovered from the vehicle""s exhaust gas system. While Benz refers more specifically to the operation of a diesel engine, it is well known that today""s gasoline engines operate at close to stoichiometric fuel-air levels, i.e., very little free oxygen is present in the vehicle""s exhaust.
A major limitation of the Benz et al approach is the difficulty in condensing water under the conditions desribed. For example, a gasoline-type fuel is arbitrarily represented to have a chemical composition corresponding to octane, C8H18, or in shorthand, CH2.25, then 3.125 atoms of oxygen are required for complete combustion of the fuel to give carbon dioxide (CO2) and water vapor (H2O). While in practice combustion is not complete, in a modem engine with emphasis on reduction of exhaust emissions it is very nearly so, so that this approximation will serve.
Oxygen (O2) comprises approximately 21% by volume of dry air, the remainder being the inert gas nitrogen with about 1% argon and other inert trace gases. Ambient air at 25xc2x0 C. at 60% of its saturation level with water vapor contains 1.88% by volume of water vapor. The amount varies with temperature and degree of saturation, but it never exceeds 6.5% under extreme tropical conditions. Thus, typical 25xc2x0 C. ambient air has the composition 20.6% by volume oxygen, 77.5% inert gases, and about 1.9% water vapor, which also corresponds to its molecular composition. 20.6 molecules (41.2 atoms) of oxygen will combust 13.184 (CH2.25) units, giving 13.184 molecules of CO2 and 14.832 molecules of H2O. The exhaust gas will therefore have a rounded composition of 13.2 CO2, 16.7 H2O, and 77.5 inert gases, giving a total of 107.4 molecules from the original 100 of air. The exhaust gas therefore contains 15.5% by volume of water vapor. When the engine in the vehicle is operating, the exhaust gas is extremely hot, therefore water recovery will require cooling, since condensation will not start to occur until it is cooled to 55xc2x0 C. Under extreme tropical conditions, a similar calculation shows that the corresponding exhaust gas composition contains a total of about 19.3% H2O, which will require a condensation temperature of less than 59.6xc2x0 C. The total water requirement for the Benz et al. disclosure under cruise conditions is 0.035 kg of water per hour, which is continuously removed from the exhaust gas produced by the engine. At a probable fuel consumption of 28 mpg (11.9 km/liter, 17.0 km/kg) under 92.2 km/hr (maximum) FTP cycle conditions, the maximum speed of this cycle, fuel consumption is about 5.42 kg per hour.
This amount of fuel yields 7.7 kg of water when combusted. Hence, less than 0.5% of the water produced need be collected. However, exhaust gas from a hot engine is at a high temperature, in excess of 350xc2x0 C., and means must be found to cool about 78.4 kg per hour of exhaust gas from this temperature to 55xc2x0 C. (under the stated 25xc2x0 C. ambient temperature conditions) to condense some of the water. Actual condensation of the small amount of water required will require the removal of about {fraction (1/1000)} of the heat removed from the hot gas. The latter will require 25xc2x0 C. ambient air in a quantity equal to about 10 times the weight of the exhaust gas per hour. Under 34.1 km/hr (maximum) FTP cycle conditions, internal combustion engine characteristics are such that the fuel consumption (in mpg, km/liter, or km/kg) will not change much, so that at the maximum speed of this cycle the fuel consumed is about 2.0 kg per hour, and the quantities of water vapor and total exhaust gas produced must be correspondingly less, namely 2.85 and 28.9 kg per hour. The quantity of exhaust gas to be handled at a steady 92.2 kph is 68,000 liters of exhaust gas per hour (about 19 liters per second). This must be handled in such a way as to cause no back-pressure on the engine. The necessary exhaust gas-to-air heat exchanger will require a very large surface area for effective heat transfer to take place. In general, the amount of heat rejected from the engine in the form of hot exhaust gas from an internal combustion engine is as much as three times the amount rejected from the liquid-cooled radiator. Since the exhaust gas-to-air heat exchanger (condenser-radiator) must work under similar conditions to this radiator (i.e., under all practical operating conditions, including idle, and all outdoor temperatures), and will have a similar heat rejection temperature to air, a very large radiator will be required. This solution is therefore not practical.
Therefore, there is a need for a reliable water supply for the automotive electrolyzer. It would be desirable if the water supply were replenishable without human involvement. It would be even more desirable if the water could be supplied in sufficient quantities to support hydrogen generation and storage for use during cold starts and/or for continuous use combating nitrogen oxide emissions.
The present invention provides a self-replenishing water source for an electrolyzer onboard an automobile comprising a condensate collection reservoir; and a means of transferring the water having an inlet in fluid communication with the condensate reservoir and an outlet in fluid communication with a water reservoir. The condensate collection reservoir may be located in the muffler or in the tail pipe. Furthermore, the water source may further comprise a filter and either a deionization bed or a distillation apparatus in fluid communication between the condensate reservoir outlet and the water reservoir.
The invention also provides an on-board hydrogen generation system, comprising: a condensate collection reservoir; a conduit providing fluid communication between the condensate collection reservoir and an anode water reservoir; an electrolyzer having an anode in communication with the anode water reservoir, a cathode, and a proton exchange membrane disposed between the anode and the cathode; and a source of electrical current having a positive terminal coupled to the anode and a negative terminal coupled to the cathode.
Further, the invention provides a method for providing water to an electrolyzer on board an automobile comprising the steps of: condensing water vapor to form a condensate; collecting the condensate; and supplying the condensate to the electrolyzer. Water vapor may be condensed in some region of the exhaust system using cooling fluid from the radiator system. The method may further comprise filtering and purifying the water and may also further comprise storing the water in a water storage reservoir.